Global Routing Operations J. Snijders
Internet-Draft J. Heasley
Intended status: Informational NTT
Expires: September 13, 2017 M. Schmidt
i3D.net
March 12, 2017
Usage of BGP Large Communities
draft-ietf-grow-large-communities-usage-03
Abstract
Examples and inspiration for operators for the use of BGP Large
Communities.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 13, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Snijders, et al. Expires September 13, 2017 [Page 1]
Internet-Draft Usage of BGP Large Communities March 2017
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. The Design Overview . . . . . . . . . . . . . . . . . . . . . 2
2.1. Informational Communities . . . . . . . . . . . . . . . . 4
2.2. Action Communities . . . . . . . . . . . . . . . . . . . 4
3. Examples of Informational Communities . . . . . . . . . . . . 5
3.1. Location . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1.1. An ISO 3166-1 numeric function . . . . . . . . . . . 5
3.1.2. A UN M.49 Region function . . . . . . . . . . . . . . 5
3.2. Relation Function . . . . . . . . . . . . . . . . . . . . 6
3.3. Combining Informational Communities . . . . . . . . . . . 6
4. Examples of Action Communities . . . . . . . . . . . . . . . 7
4.1. Selective NO_EXPORT . . . . . . . . . . . . . . . . . . . 7
4.1.1. ASN Based Selective NO_EXPORT . . . . . . . . . . . . 7
4.1.2. Location Based Selective NO_EXPORT . . . . . . . . . 7
4.2. Selective AS_PATH Prepending . . . . . . . . . . . . . . 8
4.2.1. ASN Based Selective AS_PATH Prepending . . . . . . . 8
4.2.2. Location Based Selective AS_PATH Prepending . . . . . 9
4.3. Manipulation of the LOCAL_PREF attribute . . . . . . . . 9
4.3.1. Global Manipulation of LOCAL_PREF . . . . . . . . . . 10
4.3.2. Location Based Manipulation of LOCAL_PREF . . . . . . 10
4.3.3. Note of Caution for LOCAL_PREF Functions . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . 12
8.2. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
BGP Large Communities [RFC8092] provide a mechanism to signal opaque
information between Autonomous Systems. This document presents
examples of how operators might utilise BGP Large Communities to
achieve various goals. This document draws from experience of
operational communities such as NANOG [1] and NLNOG [2].
2. The Design Overview
BGP Large Communities are composed of three 4-octet fields. The
first is the Global Administrator (GA) field, whose value is the
Autonomous System Number (ASN) of the Autonomous System (AS) that has
defined the meaning of the remaining two 4-octet fields, known as
"Local Data Part 1" and "Local Data Part 2". This document describes
an approach where the "Local Data Part 1" field contains a function
identifier and the "Local Data Part 2" contains a parameter value.
Snijders, et al. Expires September 13, 2017 [Page 2]
Internet-Draft Usage of BGP Large Communities March 2017
Using the canonical notation the above can be summarized as
"ASN:Function:Parameter".
+----------------------+---------------+
| RFC 8092 | this document |
+----------------------+---------------+
| Global Administrator | ASN |
| Local Data Part 1 | Function |
| Local Data Part 2 | Parameter |
+----------------------+---------------+
A mapping table on the usage of fields in BGP Large Communities
between [RFC8092] and this document.
Table 1: Field mapping
In contemporary deployments of both BGP Communities [RFC1997] and BGP
Large Communities, the function of a community can be divided into
two categories:
o Informational Communities
o Action Communities
Throughout the document a topology of four Autonomous Systems is used
to illustrate the usage of Communities in the following
configuration:
AS 65551
|
^
|
AS 64497
/ \
^ \
/ ^
AS 64498 \
| |
`<->- AS 64499
AS 64497 obtains transit services from (is a customer of) AS 65551, a
32-bit ASN. AS 64497 provides transit services to both AS 64498 and
AS 64499. AS 64498 and AS 64499 maintain a peering relationship in
which they only exchange their customer routes.
The opaque nature of BGP Large Communities allows for rapid
deployment of new features or changes to products. Operators are
encouraged to publicly publish and maintain documentation of the
Snijders, et al. Expires September 13, 2017 [Page 3]
Internet-Draft Usage of BGP Large Communities March 2017
purpose of each BGP Large Community, both informational and action,
that they support or are visible in BGP RIBs.
2.1. Informational Communities
Informational Communities are labels for attributes such as the
origin of the route announcement, the nature of the relation with an
EBGP neighbor or the intended propagation audience. Informational
Communities can also assist in providing valuable information for
day-to-day network operations such as debugging or capacity planning.
The Global Administrator field is set to the ASN which labels the
routes with the Informational Communities. For example, AS 64497
might add a community with the GA 64497 to a route accepted from an
IBGP or EBGP neighbor as a means of signaling that it was imported in
a certain geographical region.
In general, the intended audiences of Informational Communities are
downstream networks and the Global Administrator itself, but any
Autonomous System could benefit from receiving these communities.
2.2. Action Communities
Action Communities are added as a label to request non-default
treatment of a route within an AS. The operator of that AS defines
routing policy which, based upon the communities, adjusts route
attributes such as its propagation characteristics, the LOCAL_PREF
(local preference), the next-hop, or the number of AS_PATH prepends
to be added upon reception or propagation.
The Global Administrator field is set to the ASN which has defined
the functionality of that BGP Large Community and is therefore the
ASN that is expected to perform the action. For instance, AS 64499
might label a route with a BGP Large Community containing GA 64497 to
request that AS 64497 perform a pre-defined action upon that route.
In general, the intended audience of Action Communities are transit
providers taking action on behalf of a customer or the Global
Administrator itself, but any AS could take action if they chose and
any AS could add an action community with the GA of a non-adjacent
ASN. However, note that an Action Community could also be
informational. Its presence is an indicator that the GA may have
performed the action and that an AS in the AS_PATH requested it.
Snijders, et al. Expires September 13, 2017 [Page 4]
Internet-Draft Usage of BGP Large Communities March 2017
3. Examples of Informational Communities
3.1. Location
An AS, AS 64497 in these examples, may inform other networks about
the geographical region where AS 64497 imported a route by labeling
it with BGP Large Communities following one of the following schemes
or a combination thereof.
3.1.1. An ISO 3166-1 numeric function
AS 64497 could assign a value of 1 to the Function field to designate
the content of the Parameter field as an ISO-3166-1 [3] numeric
country identifier.
+---------------------+---------------------------------------------+
| BGP Large Community | Description |
+---------------------+---------------------------------------------+
| 64497:1:528 | Route learned in the Netherlands |
| 64497:1:392 | Route learned in Japan |
| 64497:1:840 | Route learned in the United States of |
| | America |
+---------------------+---------------------------------------------+
Example documentation for Informational Communities deployed by AS
64497 to describe the location where a route was imported using ISO
3166-1 numeric identifiers.
Table 2: Information: ISO 3166-1
3.1.2. A UN M.49 Region function
AS 64497 could assign a value of 2 to the Function field to designate
the content of the Parameter field as the M.49 numeric code published
by the United Nations Statistics Division (UNSD) [4] for macro
geographical (continental) regions, geographical sub-regions, or
selected economic and other groupings.
Snijders, et al. Expires September 13, 2017 [Page 5]
Internet-Draft Usage of BGP Large Communities March 2017
+---------------------+-------------------------------+
| BGP Large Community | Description |
+---------------------+-------------------------------+
| 64497:2:2 | Route learned in Africa |
| 64497:2:9 | Route learned in Oceania |
| 64497:2:145 | Route learned in Western Asia |
| 64497:2:150 | Route learned in Europe |
+---------------------+-------------------------------+
Example documentation for Informational Communities deployed by AS
64497 to describe the location where a route was imported using M.49
numeric codes published by the United Nations Statistics Division.
Table 3: Information: UNSD Regions
3.2. Relation Function
An AS, AS 64497 in this example, could assign a value of 3 to the
Function field to designate the content of the Parameter field as a
number indicating whether the route originated inside its own network
or was learned externally, and if learned externally, it might
simultaneously characterize the nature of the relation with that
specific EBGP neighbor.
+---------------------+---------------------------------------+
| BGP Large Community | Description |
+---------------------+---------------------------------------+
| 64497:3:1 | Route originated internally |
| 64497:3:2 | Route learned from a customer |
| 64497:3:3 | Route learned from a peering partner |
| 64497:3:4 | Route learned from a transit provider |
+---------------------+---------------------------------------+
Example documentation for Informational Communities deployed by AS
64497 to describe the relation to the ASN from which the route was
learned.
Table 4: Information: Relation
3.3. Combining Informational Communities
A route may be labeled with multiple Informational Communities. For
example, a route learned in the Netherlands from a customer might be
labeled with communities 64497:1:528, 64497:2:150 and 64497:3:2 at
the same time.
Snijders, et al. Expires September 13, 2017 [Page 6]
Internet-Draft Usage of BGP Large Communities March 2017
4. Examples of Action Communities
4.1. Selective NO_EXPORT
As part of an agreement, often a commercial transit agreement,
between AS 64497 and AS 64498, AS 64497 might expose BGP traffic
engineering functions to AS 64498. One such BGP traffic engineering
function could be selective NO_EXPORT, which is the selective
filtering of a route learned from one AS, AS 64498, to certain EBGP
neighbors of the GA, AS 64497.
4.1.1. ASN Based Selective NO_EXPORT
AS 64497 could assign a value of 4 to the Function field to designate
the content of the Parameter field as a neighboring ASN to which a
route should not be propagated.
+---------------------+---------------------------------+
| BGP Large Community | Description |
+---------------------+---------------------------------+
| 64497:4:64498 | Do not export route to AS 64498 |
| 64497:4:64499 | Do not export route to AS 64499 |
| 64497:4:65551 | Do not export route to AS 65551 |
+---------------------+---------------------------------+
Example documentation for Action Communities deployed by AS 64497 to
expose a BGP traffic engineering function which selectively prevents
the propagation of routes to the neighboring ASN specified in the
Parameter field.
Table 5: Action: ASN NO_EXPORT
4.1.2. Location Based Selective NO_EXPORT
AS 64497 could assign a value of 5 to the Function field to designate
the content of the Parameter field as an ISO 3166-1 numeric country
identifier within which a labeled route is not propagated to EBGP
neighbors. However this might not prevent one of those EBGP
neighbors from learning that route in another country and thereby
making it available in the country specified by the BGP Large
Community.
Snijders, et al. Expires September 13, 2017 [Page 7]
Internet-Draft Usage of BGP Large Communities March 2017
+-----------------+-------------------------------------------------+
| BGP Large | Description |
| Community | |
+-----------------+-------------------------------------------------+
| 64497:5:528 | Do not export to EBGP neighbors in the |
| | Netherlands |
| 64497:5:392 | Do not export to EBGP neighbors in Japan |
| 64497:5:840 | Do not export to EBGP neighbors in the United |
| | States of America |
+-----------------+-------------------------------------------------+
Example documentation for Action Communities deployed by AS 64497 to
expose a BGP traffic engineering function which selectively prevents
the propagation of routes to all EBGP neighbors in the geographical
region specified in the Parameter field.
Table 6: Action: NO_EXPORT in Region
4.2. Selective AS_PATH Prepending
As part of an agreement between AS 64497 and AS 64498, AS 64497 might
expose BGP traffic engineering functions to AS 64498. One such BGP
traffic engineering function could be selective prepending of the
AS_PATH with AS 64497 to certain certain EBGP neighbors of AS 64497.
4.2.1. ASN Based Selective AS_PATH Prepending
AS 64497 could assign a value of 6 to the Function field to designate
the content of the Parameter field as a neighboring ASN to which
prepending of the AS_PATH with AS 64497 is requested upon propagation
of the route. Additional AS_PATH Prepending functions might also be
defined to support multiples of prepending, that is two, three or
more prepends of AS 64497.
+---------------------+------------------------------------------+
| BGP Large Community | Description |
+---------------------+------------------------------------------+
| 64497:6:64498 | Prepend 64497 once on export to AS 64498 |
| 64497:6:64499 | Prepend 64497 once on export to AS 64499 |
| 64497:6:65551 | Prepend 64497 once on export to AS 65551 |
+---------------------+------------------------------------------+
Example documentation for Action Communities deployed by AS 64497 to
expose a BGP traffic engineering function which selectively prepends
the AS_PATH with AS 64497 when propagating the route to the specified
EBGP neighbor.
Table 7: Action: Prepend to ASN
Snijders, et al. Expires September 13, 2017 [Page 8]
Internet-Draft Usage of BGP Large Communities March 2017
4.2.2. Location Based Selective AS_PATH Prepending
AS 64497 could assign a value of 7 to the Function field to designate
the content of the Parameter field as an ISO 3166-1 numeric country
identifier to which the prepending of the AS_PATH with AS 64497 is
requested upon propagation of the route to all EBGP neighbors in that
region.
+------------------+------------------------------------------------+
| BGP Large | Description |
| Community | |
+------------------+------------------------------------------------+
| 64497:7:528 | Prepend once to EBGP neighbors in the |
| | Netherlands |
| 64497:7:392 | Prepend once to EBGP neighbors in Japan |
| 64497:7:840 | Prepend once to EBGP neighbors in United |
| | States of America |
+------------------+------------------------------------------------+
Example documentation for Action Communities deployed by AS 64497 to
expose a BGP traffic engineering function which selectively prepends
the AS_PATH with AS 64497 when propagating the route to all EBGP
neighbors in the geographical region specified in the Parameter
field.
Table 8: Action: Prepend in Region
4.3. Manipulation of the LOCAL_PREF attribute
As part of an agreement between AS 64497 and AS 64498, AS 64497 might
expose BGP traffic engineering functions to AS 64498. One such BGP
traffic engineering function might allow AS 64498 to manipulate the
value of the LOCAL_PREF attribute of routes learned from AS 64498
within AS 64497, even though the LOCAL_PREF attribute is non-
transitive and therefore is not propagated to EBGP neighbors.
The LOCAL_PREF value of routes are locally significant within each
Autonomous System and therefore are impossible to list in this
document. Instead, the typical LOCAL_PREF values could be classified
as a hierarchy and a BGP Large Community function exposed allowing an
EBGP neighbor to affect the LOCAL_PREF value within the specified GA.
The following non-exhaustive list defines the classes of routes in
the order of descending LOCAL_PREF value and assigns a function
identifier which could be used in the Function field of a BGP Large
Community.
Snijders, et al. Expires September 13, 2017 [Page 9]
Internet-Draft Usage of BGP Large Communities March 2017
+----------+--------------------------------------------------------+
| Function | Preference Class |
+----------+--------------------------------------------------------+
| 8 | Normal customer route. |
| 9 | Backup customer route. |
| 10 | Peering route. |
| 11 | Upstream transit route. |
| 12 | Fallback route, to be installed if no other path is |
| | available. |
+----------+--------------------------------------------------------+
Table 9: Action: Preference Function Identifiers
4.3.1. Global Manipulation of LOCAL_PREF
AS 64497 could place one of the previously defined Preference
Function Identifiers in the Function field and set the value 0 in the
Parameter field to designate that the LOCAL_PREF associated with that
function identifier should be applied for that route throughout the
whole Autonomous System.
+---------------------+---------------------------------------------+
| BGP Large Community | Description |
+---------------------+---------------------------------------------+
| 64497:9:0 | Assign LOCAL_PREF for a customer backup |
| | route |
| 64497:10:0 | Assign LOCAL_PREF for a peering route |
| 64497:12:0 | Assign LOCAL_PREF for a fallback route |
+---------------------+---------------------------------------------+
Example documentation for Action Communities deployed by AS 64497 to
expose a BGP traffic engineering function which allows a BGP neighbor
to globally manipulate the LOCAL_PREF attribute for the route within
AS 64497.
Table 10: Action: Global LOCAL_PREF Manipulation
4.3.2. Location Based Manipulation of LOCAL_PREF
AS 64497 could place one of the previously defined Preference
Function Identifiers in the Function field and use an ISO 3166-1
numeric country identifier in the Parameter field to designate the
geographical region within which the non-default LOCAL_PREF
associated with that function identifier should be applied to the
route. The value of the LOCAL_PREF attribute should not deviate from
the default for that route class in any region not specified by one
or more of these Action Communities.
Snijders, et al. Expires September 13, 2017 [Page 10]
Internet-Draft Usage of BGP Large Communities March 2017
+--------------+----------------------------------------------------+
| BGP Large | Description |
| Community | |
+--------------+----------------------------------------------------+
| 64497:9:528 | Assign LOCAL_PREF for a customer backup route on |
| | BGP speakers in the Netherlands |
| 64497:10:392 | Assign LOCAL_PREF for a peering route on BGP |
| | speakers in Japan |
| 64497:12:840 | Assign LOCAL_PREF for a fallback route on BGP |
| | speakers in United States of America |
+--------------+----------------------------------------------------+
Example documentation for Action Communities deployed by AS 64497 to
expose a BGP traffic engineering function which allows a BGP neighbor
to selectively manipulate the LOCAL_PREF attribute within AS 64497 in
the geographical region specified in the Parameter field.
Table 11: Action: Regional LOCAL_PREF Manipulation
4.3.3. Note of Caution for LOCAL_PREF Functions
The LOCAL_PREF attribute strongly influences the BGP Decision
Process, which in turn affects the scope of route propagation.
Therefore, Operators should take special care when using Action
Communities that decrease the LOCAL_PREF value, and therefore the
degree of preference, to a value below that of another route class.
Some of the unintended BGP states that might arise as a result of
these traffic engineering decisions are described as "BGP Wedgies" in
[RFC4264].
5. Security Considerations
Network operators should note the recommendations in Section 11 of
BGP Operations and Security [RFC7454].
6. IANA Considerations
None.
7. Acknowledgments
The authors would like to gratefully acknowledge the insightful
comments, contributions, critique and support from Adam Chappell,
Jonathan Stewart, and Will Hargrave.
Snijders, et al. Expires September 13, 2017 [Page 11]
Internet-Draft Usage of BGP Large Communities March 2017
8. References
8.1. Normative References
[RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities
Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
<http://www.rfc-editor.org/info/rfc1997>.
[RFC4264] Griffin, T. and G. Huston, "BGP Wedgies", RFC 4264,
DOI 10.17487/RFC4264, November 2005,
<http://www.rfc-editor.org/info/rfc4264>.
[RFC7454] Durand, J., Pepelnjak, I., and G. Doering, "BGP Operations
and Security", BCP 194, RFC 7454, DOI 10.17487/RFC7454,
February 2015, <http://www.rfc-editor.org/info/rfc7454>.
[RFC8092] Heitz, J., Ed., Snijders, J., Ed., Patel, K., Bagdonas,
I., and N. Hilliard, "BGP Large Communities Attribute",
RFC 8092, DOI 10.17487/RFC8092, February 2017,
<http://www.rfc-editor.org/info/rfc8092>.
8.2. URIs
[1] http://nanog.net
[2] http://nlnog.net
[3] https://www.iso.org/iso-3166-country-codes.html
[4] https://unstats.un.org/unsd/methodology/m49/
Authors' Addresses
Job Snijders
NTT Communications
Theodorus Majofskistraat 100
Amsterdam 1065 SZ
The Netherlands
Email: job@ntt.net
Snijders, et al. Expires September 13, 2017 [Page 12]
Internet-Draft Usage of BGP Large Communities March 2017
John Heasley
NTT Communications
1111 NW 53rd Drive
Portland, OR 97210
United States of America
Email: heas@shrubbery.net
Martijn Schmidt
i3D.net
Rivium 1e Straat 1
Capelle aan den IJssel 2909 LE
NL
Email: martijnschmidt@i3d.net
Snijders, et al. Expires September 13, 2017 [Page 13]